Dehydrogenation of alkanols to increase yield of aromatics

ABSTRACT

The present invention provides methods, reactor systems, and catalysts for increasing the yield of aromatic hydrocarbons produced while converting alkanols to hydrocarbons. The invention includes methods of using catalysts to increase the yield of benzene, toluene, and mixed xylenes in the hydrocarbon product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/304,052 filed on Nov. 23, 2011, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present invention is directed to catalysts and methods forincreasing aromatic yield in processes for converting alkanols tohydrocarbons.

BACKGROUND OF THE INVENTION

Aromatic hydrocarbons, notably benzene, toluene and ortho- andpara-xylene (collectively, mixed xylenes), are important industrialcommodities used, for example, to produce numerous chemicals, fibers,plastics, and polymers, including styrene, phenol, aniline, polyester,and nylon.

Mixtures of aromatic- and paraffinic hydrocarbons can be produced byconverting alkanols in the presence of an oxygenate conversion catalyst,such as a zeolite catalyst. For example, methanol can be converted togasoline range paraffins, aromatics, and olefins. Higher alcohols, suchas ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol,tert-butyl alcohol, pentanol, and hexanol, can also be converted tohydrocarbons using this process.

When oxygenates are converted to hydrocarbons in the presence of azeolite catalyst, the hydrogen-to-carbon effective ratio (H:C_(eff)ratio) of the reactants affects the H:C_(eff) ratio of the reactionproducts. The H:C_(eff) ratio is calculated as follows:

${{H:C_{eff}} = \frac{H - {2O}}{C}},$where H represents the number of hydrogen atoms, O represents the numberof oxygen atoms, and C represents the number of carbon atoms. Water andmolecular hydrogen (diatomic hydrogen, H₂) are excluded from thecalculation. The H:C_(eff) ratio applies both to individual componentsand to mixtures of components, but is not valid for components whichcontain atoms other than carbon, hydrogen, and oxygen. For mixtures, theC, H, and O are summed over all components exclusive of water andmolecular hydrogen. The term “hydrogen” refers to any hydrogen atomwhile the term “molecular hydrogen” is limited to diatomic hydrogen, H₂.For illustration purposes, the H:C_(eff) ratio of ethanol (and of allalkanols) is 2, as shown in Table 1 below.

TABLE 1 H:C_(eff) Ratio of Alcohols Alcohol (by number of carbon atoms)H:C_(eff) C 2 C₂ 2 C₃ 2 C₄ 2 C₅ 2 C₆ 2 C₇ 2 C₈ 2 C₉ 2 ↓ ↓ C_(∞) 2

Paraffins generally have a H:C_(eff) ratio greater than 2, while alkylmono-aromatic compounds generally have a H:C_(eff) ratio between 1 and2, as shown in Tables 2 and 3 below.

TABLE 2 H:C_(eff) Ratio of Paraffins Paraffins H:C_(eff) C₁ 4 C₂ 3 C₃2.67 C₄ 2.5 C₅ 2.4 C₆ 2.33 C₇ 2.29 C₈ 2.25 C₉ 2.22 ↓ ↓ C_(∞) 2

TABLE 3 H:C_(eff) Ratio of Alkyl Substituted Mono-Aromatics AromaticH:C_(eff) Benzene 1.0 Toluene 1.14 Xylene 1.25 C₉ 1.33 ↓ ↓ C_(∞) 2

Other species of interest include carbon dioxide (CO₂) with a H:C_(eff)ratio of −4, carbon monoxide (CO) with a H:C_(eff) ratio of −2, andcarbon (C) with a H:C_(eff) ratio of 0. Carbonaceous residue, or coke,that may accumulate on catalyst or other surfaces exhibits a range ofH:C_(eff) ratios, depending on the amount of residual hydrogen andoxygen within the coke.

For the conversion of alkanols to hydrocarbons, many feeds of interestare essentially free of atoms other than C, H, and O, allowing from apractical standpoint the characterization of the feed to a reaction stepusing the H:C_(eff) ratio and the products of a reaction step using theH:C_(eff) ratio. For instance, alkanols can react across zeolitecatalysts to form a mixture of hydrocarbons. Because of the highH:C_(eff) ratio of alkanols, conversion of alkanols across zeolitecatalysts generally yields a relatively high ratio of paraffins toaromatics—approximately three moles of paraffins are generated per moleof benzene or alkyl-substituted mono-aromatics. This is a desirablemixture for some applications, such as gasoline production. However, thelow yield of aromatics limits the application of this process for theproduction of high value aromatic chemicals such as benzene, toluene,and xylenes (BTX).

Zhang et al. recently studied the impact of the H:C_(eff) ratio on theconversion of biomass-derived feedstocks to coke, olefins and aromaticsusing a ZSM-5 catalyst (Zhang et al., Catalytic conversion ofbiomass-derived feedstocks into olefins and aromatics with ZSM-5: thehydrogen to carbon effective ratio, Energy Environ. Sci., 2011, 4,2297). In this study, Zhang reported that biomass derived feedstockshaving H:C_(eff) ratios of between 0 and 0.3 produced high levels ofcoke, making it uneconomical to convert biomass derived feedstocks toaromatics and chemicals. Zhang also reported that the aromatic+olefinyield increases and the coke yield decreases with increasing H:C_(eff)ratio of the feed. However, there is an inflection point at a H:C_(eff)ratio of 1.2, where the aromatic+olefin yield does not increase asrapidly. The ratio of olefins to aromatics also increases withincreasing H:C_(eff) ratio, while CO and CO₂ yields go through a maximumwith increasing H:C_(eff) ratio. Specifically, Zhang reported that thearomatic and olefin yields increased from 12% and 15% to 24% and 56%with increasing H:C_(eff) ratio, respectively, and that the olefin yieldis higher than the aromatic yield for all feedstocks, with the gapincreasing with an increase of the H:C_(eff) ratio. Once again, this lowyield of aromatics limits the application of the Zhang process for theproduction of high value aromatic chemicals such as benzene, toluene,and xylenes (BTX).

There remains a need for a method to increase the yield of aromatichydrocarbons produced when converting alkanols to hydrocarbons.

SUMMARY OF THE INVENTION

The invention provides methods for converting alkanols to aromatichydrocarbons. The method generally involves: (1) exposing an alkanolfeedstock to a dehydrogenation catalyst at a dehydrogenation temperatureand a dehydrogenation pressure to produce hydrogen and an oxygenatecomponent; and (2) exposing the oxygenate component to an oxygenateconversion catalyst at an oxygenate conversion temperature and anoxygenate conversion pressure to produce aromatic hydrocarbons.

One aspect of the invention is that the oxygenate component has adesired hydrogen to carbon effective ratio (H:C_(eff) ratio). In oneembodiment, the oxygenate component has a hydrogen to carbon effectiveratio of less than 2.0, 1.9, 1.8, 1.7 or 1.6. In another embodiment, theoxygenate component has a hydrogen to carbon effective ratio of greaterthan 1.0, 1.1, 1.2, 1.3 1.4 or 1.5. In yet another embodiment, theoxygenate component has a hydrogen to carbon effective ratio between 1.0and 1.8, or 1.2 and 1.7.

When the dehydrogenation and oxygenate conversion are complete, some ofthe carbon from the alkanol feedstock is contained within the aromatichydrocarbons. In one embodiment, more than 40% of carbon in the alkanolfeedstock is contained within the aromatic hydrocarbon product. Inanother embodiment, more than 45% of carbon in the alkanol feedstock iscontained within the aromatic hydrocarbon product.

Another aspect of the invention is the composition of the alkanolfeedstock. In one embodiment the alkanol feedstock is derived frommaterial of recent biological origin such that the age of the compounds,or fractions containing the compounds, is less than 100 years old,preferably less than 40 years old, and more preferably less than 20years old, as calculated from the carbon 14 concentration of thefeedstock. In other embodiments, the alkanol feedstock comprises aprimary alcohol, ethanol, n-butanol, 2-butanol, or isobutanol. In otherembodiments, the alkanol feedstock is derived from a fermentation,Fischer-Tropsch, pyrolysis, aqueous phase reforming or other catalyticconversion process.

When the alkanol feedstock is exposed to a dehydrogenation catalyst at adehydrogenation temperature and pressure, hydrogen and an oxygenatecomponent are produced. In one embodiment, the oxygenate componentcomprises a carboxylic acid, an aldehyde, and an ester. In otherembodiments, the oxygenate component comprises a carboxylic acid and anester, or the oxygenate component comprises an aldehyde.

The dehydrogenation catalyst is capable of dehydrogenating alkanols toform the oxygenate component. In one embodiment, the dehydrogenationcatalyst comprises a metal selected from the group consisting of Cu, Ru,Ag, CuCr, CuZn, Co, alloys thereof, and combinations thereof. Thedehydrogenation catalyst may further comprise a support. The support maycomprise a material selected from the group consisting of alumina,silica, silica-alumina, titania, carbon, zirconia, and mixtures thereof.In one embodiment, the dehydrogenation catalyst comprises Cu on a silicasupport. In another embodiment, the dehydrogenation catalyst comprisesRaney copper or copper zinc aluminate.

The dehydrogenation reaction is conducted at a temperature and pressurewhere the thermodynamics are favorable. In one embodiment, thedehydrogenation temperature is between about 80° C. and 500° C., and thedehydrogenation pressure ranges from below atmospheric pressure to about1000 psig.

The aromatic hydrocarbons are produced by catalytically reacting theoxygenate component in the presence of an oxygenate conversion catalystat a oxygenate conversion temperature and an oxygenate conversionpressure. In one embodiment, the oxygenate conversion catalyst comprisesa zeolite. In another embodiment, the oxygenate conversion catalyst isZSM-5. The oxygenate conversion catalyst may be modified by a materialselected from the group consisting of phosphorous, gallium, zinc,nickel, tungsten, and mixtures thereof. The oxygenate conversioncatalyst may also contain a binder selected from the group consisting ofalumina, silica, silica-alumina, titania, zirconia, aluminum phosphate,and mixtures thereof.

The oxygenate conversion reaction is conducted at a temperature andpressure where the thermodynamics are favorable. In one embodiment, theoxygenate conversion temperature is between about 250° C. and 550° C.,and the oxygenate conversion pressure ranges from less than atmosphericpressure to about 1000 psig.

Another aspect of the invention is a method of producing hydrocarbons bycatalytically reacting an alkanol feedstock with a multi-functionaldehydrogenation/oxygenate conversion catalyst at a temperature andpressure suitable to produce hydrocarbons.

Yet another aspect of the invention is a method of producing aromatichydrocarbons comprising the steps or acts of: (1) exposing a feedstockcomprising a first oxygenate component to a dehydrogenation catalyst ata dehydrogenation temperature and a dehydrogenation pressure to producehydrogen and a second oxygenate component, and (2) exposing the secondoxygenate component to an oxygenate conversion catalyst at an oxygenateconversion temperature and an oxygenate conversion pressure to producearomatic hydrocarbons.

Another aspect of the invention is a method of converting ethanol toaromatic hydrocarbons, the method comprising the steps or acts of: (1)exposing an ethanol feedstock to a dehydrogenation catalyst at adehydrogenation temperature and a dehydrogenation pressure to produce areaction stream comprising acetaldehyde, acetic acid, and ethyl acetate,and (2) exposing the reaction stream to an oxygenate conversion catalystat an oxygenate conversion temperature and an oxygenate conversionpressure to produce aromatic hydrocarbons.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the chemistry involved in one aspect of thepresent invention using ethanol as the feedstock.

FIG. 2 is a chart illustrating increased aromatic yield in the claimedprocess versus traditional methods of converting alcohols tohydrocarbons as a function of the hydrogen-to-carbon effective ratio.

FIG. 3 is chart illustrating the shift in liquid product compositionassociated with a decreased hydrogen-to-carbon effective ratio.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods, reactor systems, and catalystsfor increasing the yield of aromatic hydrocarbons produced whileconverting alkanols to hydrocarbons. The invention includes methods ofusing catalysts to increase the yield of benzene, toluene, and mixedxylenes in the hydrocarbon product.

As used herein, the term “alkanols” refers to, without limitation,aliphatic alcohols with the general formula C_(n) H_(2n+2)O₁. Alkanolssuitable for use in feedstocks in accord with the invention include C₁to C₆ alkanols, which can be primary or secondary alcohols, such as oneor more of methanol, ethanol, n-propanol, iso-propanol, n-butanol,2-butanol, isobutanol, n-pentanol, or n-hexanol. Tertiary alcohols areless preferred as sole components of an alkanol feedstock, but can beused when combined with more suitable primary or secondary alcohols.

The alkanols may originate from any source, but are preferably derivedfrom biomass. As used herein, the term “biomass” refers to, withoutlimitation, organic materials produced by plants (such as leaves, roots,seeds and stalks), and microbial and animal metabolic wastes. Commonsources of biomass include: (1) agricultural wastes, such as cornstalks, straw, seed hulls, sugarcane leavings, bagasse, nutshells, andmanure from cattle, poultry, and hogs; (2) wood materials, such as woodor bark, sawdust, timber slash, and mill scrap; (3) municipal waste,such as waste paper and yard clippings; and (4) energy crops, such aspoplars, willows, switch grass, alfalfa, prairie bluestream, corn,soybean, and the like. The term also refers to the primary buildingblocks of the above, namely, saccharides, lignin, cellulosics,hemicellulose and starches, among others.

Alkanols from biomass may be produced by any known method. Such methodsinclude fermentation technologies using enzymes or microorganisms,Fischer-Tropsch reactions to produce C₂₋₁₀ alpha alcohols, and pyrolysistechnologies to produce alcohols from oil, among others. In oneembodiment, the alkanols are produced using catalytic reformingtechnologies, such as the BioForming® technology developed by Virent,Inc. (Madison, Wis.), and described in U.S. Pat. No. 7,767,867(Cortright), U.S. Pat. No. 7,898,664 (Cortright), U.S. Pat. No.8,053,615 (Cortright et al.), U.S. Pat. No. 8,017,818 (Cortright etal.), and U.S. Pat. No. 7,977,517 (Cortright et al.), all of which areincorporated herein by reference. The alkanols may also be derived fromnatural gas using Fischer-Tropsch type reactions.

Surprisingly, the inventors increased the yields of aromatichydrocarbons by partially dehydrogenating alkanol feedstocks using adehydrogenation catalyst in the below described reaction environment.Without being bound to any particular theory, the inventors believe thathydrogen atoms, made available through the conversion of relativelyhydrogen-rich alkanols to aromatics, can be transferred to unsaturatedcomponents by the catalyst. If the hydrogen is transferred to an olefin,a paraffin is generated. Because olefins are precursors to aromatics,the conversion of an olefin to a paraffin reduces the available pool ofmaterial that is able to be converted to aromatics. If the hydrogen istransferred to a ketone or aldehyde, an alkanol is formed. In thismanner, the carbonyl group of the ketone or aldehyde acts as a hydrogensink, removing reactive hydrogen and preventing the conversion ofolefins to paraffins, thereby reducing the amount of paraffins andincreasing the overall aromatics yield. The resulting alkanol is alsoproductive as it serves as additional feedstock for the hydrocarbonforming reactions.

As used herein, oxygenates capable of reacting with hydrogen in thismanner are termed “hydrogen acceptors”. It is believed that carbonyls,carboxylic acids, esters, cyclic ethers, diols, polyols, furans andother oxygenates characterized by having a H:C_(eff) ratio of <2 arecapable of being hydrogen acceptors, either directly or following otherreactions (such as dehydration), which have converted the components tohydrogen acceptors. The net impact of transferring hydrogen tounsaturated oxygenates is to produce fewer paraffins and increase thearomatic hydrocarbon yield.

In one embodiment, the alkanol is ethanol. The oxygenates produced fromethanol generally include acetaldehyde, acetic acid, and ethyl acetate.During the claimed reaction, primary alkanols produce the equivalentproducts corresponding to the carbon number of the starting alkanol.Secondary alcohols are unable to proceed to acids or esters and willproduce primarily ketones, unless used in a mixture with other alkanols.The specific products depend on various factors including thecomposition of the alkanol feedstock, reaction temperature, reactionpressure, alkanol concentration, the reactivity of the catalyst, and theflow rate of the alkanol feedstock as it affects the space velocity (themass/volume of reactant per unit of catalyst per unit of time).

Ethers may also be produced from alkanols. For instance, the conversionof methanol to dimethyl ether can be used to reduce the exotherm ofoxygenate conversion. Dialkyl ethers may also be present in the feed tothe oxygenate conversion catalyst as a product of the dehydrogenationcatalyst or as a separately fed component. Dialkyl ethers, such asdiethylether, dimethylether, etc., have a H;C_(eff) ratio of 2.0 and, assuch, impact the aromatic to paraffin ratio of the product the same asan alkanol.

As indicated above, the H:C_(eff) ratio of the reactants impacts theH:C_(eff) ratio of the reaction products. When the hydrogen acceptorsare passed as reactants over an oxygenate conversion catalyst, animproved aromatic hydrocarbon yield is realized, relative to the yieldrealized when the reactants are alkanols. The H:C_(eff) ratio of thealdehydes that may be formed by dehydrogenation of primary alkanols isbetween zero and 2 as shown in Table 4 below.

TABLE 4 H:C_(eff) Ratio of Aldehydes and Ketones Aldehydes or Ketonecarbon number H:C_(eff) C₁ 0 C₂ 1.0 C₃ 1.33 C₄ 1.5 C₅ 1.6 C₆ 1.67 C₇1.71 C₈ 1.75 C₉ 1.78 ↓ ↓ C_(∞) 2

In accordance with the invention, the process for converting alkanols tohydrocarbons can be a two-step process (in which the dehydrogenationcatalyst and the oxygenate conversion catalyst can be separatecatalysts) or a one-step process (in which the dehydrogenation catalystand the oxygenate conversion catalyst can be one multi-functionalcatalyst). When separate catalysts are provided, they may be present inseparate vessels, in separate beds within a single vessel, inalternating layers in a single bed of catalyst, or physically mixedwithin the same bed.

The general two-step process is as follows. An alkanol feedstock isfirst passed into contact with a dehydrogenation catalyst in a reactorat a dehydrogenation temperature and a dehydrogenation pressure, therebyreleasing molecular hydrogen and producing the oxygenates illustrated inFIG. 1. The alkanol feedstock may be an essentially pure alkanol streamor, alternatively, the alkanol feedstock may be mixed with water tocreate an aqueous solution wherein the alkanol concentration is greaterthan 1%, or greater than 5%, or greater than 10%, or greater than 20%,or greater than 30%, or greater than 40%, or greater than 50%.

The dehydrogenation catalyst includes one or more materials of metaland/or basic functionality capable of catalyzing the conversion ofhydroxyl elements to carbonyls. Suitable metallic components include,without limitation, Cu, Ru, Ag, CuCr, CuZn, Co, Sn, Mo, and combinationsthereof. Suitable base-catalyzed dehydrogenation catalysts include Li,Na, K, Cs, Mg, Ca, Ba, Zn, Ce, La, Y, Zr, hydrotalcite, base-treatedaluminosilicate zeolite. The base catalyst may also include an oxide ofTi, Zr, V, Mo, Cr, Mn, Al, Ga, Co, Ni, Si, Cu, Zn, Sn, Mg, P, Fe, andcombinations thereof. Preferred Group IA materials include Li, Na, K,and Cs. Preferred Group HA materials include Mg, Ca, and Ba. A preferredGroup IIB material is Zn. Preferred Group IIIB materials include Y andLa. Basic resins include resins that exhibit basic functionality, suchas Amberlyst A26 and Amberlyst A21. The base catalyst may beself-supporting or adhered to any one of the supports further describedbelow, including supports containing carbon, silica, alumina, zirconia,titania, vanadia, ceria, alloys and mixtures thereof.

The base catalyst may also include zeolites and other microporoussupports that contain Group IA compounds, such as Li, Na, K, and Cs.Preferably, the Group IA material is present in an amount greater thanthat required to neutralize the acidic nature of the support. Thesematerials may be used in any combination, and also in combination withalumina or silica. A metal function may also be provided by the additionof group VIIIB metals, or Cu, Ga, In, Zn, Cr, or Sn.

The dehydrogenation catalyst is either self-supporting or, preferably,includes a supporting material. The support for the metallic componentmay contain any one or more of alumina, silica, silica-alumina, titania,carbon, zirconia, and mixtures thereof. Copper on a silica support,Raney copper, and copper-zinc-aluminate are particularly preferreddehydrogenation catalysts. For the copper catalyst on a silica support,the copper content may generally range from 0.05% to 40%, preferablyfrom 0.1% to 20%, and most preferably from 0.2% to 10%.

In some embodiments, the dehydrogenation temperature is between about80° C. and 500° C., preferably between about 100° C. and 450° C., andmost preferably between about 150° C. and 400° C. The dehydrogenationpressure ranges from below atmospheric pressure up to about 1000 psig,preferably from about atmospheric pressure to about 700 psig, and mostpreferably from about 10 psig to about 500 psig.

The extent to which the alkanol feed stock is dehydrogenated can bemeasured by the amount of molecular hydrogen released duringdehydrogenation and may range from 0.05 to 2.0 moles of molecularhydrogen released per mole of alkanol feed. Values greater than 1 moleof molecular hydrogen released per mole of feed are possible whencarbonyls are further converted to acids, with an associated consumptionof water and release of molecular hydrogen. In general, the reactionshould be conducted under conditions where the residence time of thealkanol feedstock over the catalyst is appropriate to generate thedesired dehydrogenation products. For example, the residence time may beestablished at a weight hourly space velocity (WHSV) of between 0.01 and30, or between 0.05 and 10, or between 0.1 and 5, or between 1.0 and 4.

Desirable levels of dehydrogenation depend on the composition of thealkanol feedstock. To produce a shift in the aromatic-to-paraffin ratioduring the oxygenate conversion, longer chain alcohols must bedehydrogenated to a greater extent than short chain alcohols. For amethanol feedstock, less than 50% dehydrogenation is desirable (0.5moles of molecular hydrogen released per mole of total feedstock to thesystem), and less than 37% is preferred to prevent an excessive cokingrate. For an ethanol feedstock, less than 85% dehydrogenation isdesirable (0.85 moles of molecular hydrogen released per mole of totalfeedstock to the system), and less than 75% is preferred. For mixedalkanol feedstocks, the overall extent of dehydrogenation should be suchthat the overall H:C_(eff) ratio is less than 2.0, 1.9, 1.8, 1.7 or 1.6,and greater than 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5. For example, theoverall extent of dehydrogenation should be such that the carboneffective ratio is between 1.0 and 1.8, and preferably between 1.2 and1.7. For alkanols containing three or more carbons, any level up tocomplete dehydrogenation may be desirable. Dehydrogenation extent may becontrolled by varying the catalyst and operating conditions. Highertemperatures generally lead to greater levels of dehydrogenation.Hydrogen may be added to the reaction to limit the extent ofdehydrogenation and to prevent deactivation of the dehydrogenationcatalyst.

Other components, such as additional oxygenates and hydrogen, may beadded to the dehydrogenation products. If additional components areadded, it may be preferable to dehydrogenate smaller chain alcohols suchas methanol and ethanol to a greater extent so that the overallH:C_(eff) ratio is between 1.0 and 1.8, and preferably between 1.2 and1.7.

The dehydrogenation products, including unreacted alcohols and thehydrogen acceptors, are then passed in whole or in part into contactwith an oxygenate conversion catalyst in a reactor under conditions oftemperature and pressure effective to convert a portion of thedehydrogenation products to aromatic hydrocarbons. The oxygenateconversion catalyst has one or more acidic materials capable ofcatalyzing the conversion of dehydrogenation products to the desiredaromatic hydrocarbons. The conversion catalyst may include, withoutlimitation, aluminosilicates (zeolites), silica-alumina phosphates(SAPO), aluminum phosphates (ALPO), amorphous silica alumina, zirconia,sulfated zirconia, tungstated zirconia, titania, acidic alumina,phosphated alumina, phosphated silica, sulfated carbons, phosphatedcarbons, heteropolyacids, and combinations thereof. In one embodiment,the catalyst may also include a modifier, such as Ce, Y, Sc, La, P, B,Bi, Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, and combinations thereof. Thecatalyst may also be modified by the addition of a metal, such as Cu,Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr, Mo,W, Sn, Os, alloys and combinations thereof, to provide metalfunctionality, and/or oxides of Ti, Zr, V, Nb, Ta, Mo, Cr, W, Mn, Re,Al, Ga, In, Fe, Co, Ir, Ni, Si, Cu, Zn, Sn, Cd, P, and combinationsthereof. The conversion catalyst may be self-supporting or adhered toany one of the supports further described below, including supportscontaining carbon, silica, alumina, zirconia, titania, vanadia, ceria,heteropolyacids, alloys and mixtures thereof.

Ga, In, Zn, Fe, Mo, Ag, Au, Ni, P, Sc, Y, Ta, and lanthanides may alsobe exchanged onto zeolites to provide a zeolite catalyst. The term“zeolite” as used herein refers not only to microporous crystallinealuminosilicate but also for microporous crystalline metal-containingaluminosilicate structures, such as galloaluminosilicates andgallosilicates. Metal functionality may be provided by metals such asCu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga, In, Rh, Pd, Ir, Re, Mn, Cr,Mo, W, Sn, Os, alloys and combinations thereof.

Examples of suitable zeolite catalysts include ZSM-5, ZSM-11, ZSM-12,ZSM-22, ZSM-23, ZSM-35 and ZSM-48. Zeolite ZSM-5, and the conventionalpreparation thereof, is described in U.S. Pat. No. 3,702,886; Re. 29,948(highly siliceous ZSM-5); U.S. Pat. Nos. 4,100,262 and 4,139,600, allincorporated herein by reference. Zeolite ZSM-11, and the conventionalpreparation thereof, is described in U.S. Pat. No. 3,709,979, which isalso incorporated herein by reference. Zeolite ZSM-12, and theconventional preparation thereof, is described in U.S. Pat. No.3,832,449, incorporated herein by reference. Zeolite ZSM-23, and theconventional preparation thereof, is described in U.S. Pat. No.4,076,842, incorporated herein by reference. Zeolite ZSM-35, and theconventional preparation thereof, is described in U.S. Pat. No.4,016,245, incorporated herein by reference. Another preparation ofZSM-35 is described in U.S. Pat. No. 4,107,195, the disclosure of whichis incorporated herein by reference. ZSM-48, and the conventionalpreparation thereof, is taught by U.S. Pat. No. 4,375,573, incorporatedherein by reference. Other examples of zeolite catalysts are describedin U.S. Pat. No. 5,019,663 and U.S. Pat. No. 7,022,888, alsoincorporated herein by reference.

As described in U.S. Pat. No. 7,022,888, the acid catalyst may be abifunctional pentasil zeolite catalyst including at least one metallicelement from the group of Cu, Ag, Au, Pt, Ni, Fe, Co, Ru, Zn, Cd, Ga,In, Rh, Pd, Ir, Re, Mn, Cr, Mo, W, Sn, Os, alloys and combinationsthereof, or a modifier from the group of Ga, In, Zn, Fe, Mo, Au, Ag, Y,Sc, Ni, P, Ta, lanthanides, and combinations thereof. The zeolite may beused with reactant streams containing an oxygenated hydrocarbon at atemperature of below 600° C. The zeolite may have ZSM-5, ZSM-8 or ZSM-11type crystal structure consisting of a large number of 5-memberedoxygen-rings, i.e., pentasil rings. The zeolite with ZSM-5 typestructure is a particularly preferred catalyst.

The catalyst may optionally contain any binder such as alumina, silicaor clay material. The catalyst can be used in the form of pellets,extrudates and particles of different shapes and sizes. In one aspect,the oxygenate conversion catalysts are ZSM-5 and beta zeolite.

In general, the oxygenate conversion temperature is between about 250°C. and 550° C., preferably between about 300° C. and 500° C., and mostpreferably between about 320° C. and 480° C. The oxygenate conversionpressure ranges from below atmospheric pressure up to about 1000 psig,preferably from about atmospheric pressure to about 700 psig, and morepreferably from about 10 psig to about 500 psig. In general, thereaction should be conducted under conditions where the residence timeof the dehydrogenation products over the oxygenate conversion catalystis appropriate to generate the desired hydrocarbons. For example, theresidence time may be established at a weight hourly space velocity(WHSV) of between 0.01 and 30, or between 0.05 and 10, or between 0.1and 5, or between 1.0 and 4.

Excluding molecular hydrogen (H₂), the overall H:C_(eff) ratio of thedehydrogenation products is generally less than 2, resulting in anincreased yield of aromatics, and an improvement over traditionalmethods of converting alcohols to hydrocarbons. When the dehydrogenationand oxygenate conversion are complete, more than 40%, or 45%, or 50%, or60%, or 70%, or 75%, of the carbon in the alkanol feedstock is containedwithin the aromatic hydrocarbon product. FIG. 2 shows the improvedaromatic yield achieved by reducing the H:C_(eff) ratio below 2. FIG. 3shows the increase in liquid product aromatic content achieved byreducing the H:C_(eff) ratio below 2. Additional oxygenated feedcomponents may also be introduced into the second reactor.

The present invention may also be practiced as a one-step process inwhich the dehydrogenation catalyst and the oxygenate conversion catalystis a multi-functional catalyst. In this approach, alkanols are convertedto hydrocarbons employing a multi-functional catalyst having one or morematerials capable of catalyzing both the dehydrogenation and oxygenateconversion reactions. The multi-functional catalyst may include any ofthe elements suitable for separate dehydrogenation and oxygenateconversion catalysts discussed above. One particularly useful catalystis copper loaded onto silica-bound ZSM-5. In this single-stepembodiment, the dehydrogenation reaction and the oxygenate conversionreactions occur in the same reaction vessel under conditions oftemperature and pressure as described above and which are suitable forboth the dehydrogenation and oxygenate conversion reactions to proceed.

In some embodiments, the products of the dehydrogenation step areseparated to provide one or more streams which are directed to theconversion reactor and one or more streams which are not directly fedinto the conversion reactor. The streams which are not directly fed intothe conversion reactor may be removed from the system or recycled to thedehydrogenation reactor for further conversion. Means of separationinclude, without limitation, separation based on volatility differencesbetween components, extraction, membranes, and ion exchange. In onepreferred embodiment, the products of the dehydrogenation step arecooled and a portion of the molecular hydrogen produced in the reactionstep is removed as a gas phase product prior to sending the remainingcomponents to the conversion reactor. In another preferred embodiment,the dehydrogenation product is separated by distillation to provide analdehyde enriched stream which is recycled to the dehydrogenationreactor to effect conversion of the aldehydes to acids and esters. Inyet another preferred embodiment, Alkanols are separated from theproduct stream and recycled to the dehydrogenation reactor to increasethe overall alkanol conversion.

In other embodiments, oxygenates other than alkanols may be used inaddition to and as a supplement to the alkanol feedstock.

The following examples are to be considered illustrative of variousaspects of the invention and should not be construed to limit the scopeof the invention, which are defined by the appended claims.

EXAMPLES Preparing Ethanol Dehydrogenation Catalysts Example 1

Copper modified monoclinic zirconia was prepared by adding an aqueoussolution of copper nitrate to monoclinic zirconia (Saint-Gobain Norpro,Ohio) using an incipient wetness impregnation technique to achieve atarget copper loading of 1, 2 and 5 wt %. The catalyst was driedovernight under vacuum at 110° C. and calcined at 400° C. under flowingair for 6 hours.

Example 2

Copper nitrate (Acros, Geel, Belgium) was added to a gamma aluminasupport (Norpro Saint Gobain, Paris, France) using an incipient wetnessimpregnation technique to achieve a target Cu loading of 5 wt %. Thecatalyst was dried in an oven with an air purge at 120° C. and thencalcined in the same oven with a temperature ramp of 2° C./min to 550°C. and held for 7 hours.

Example 3

Copper modified calcium doped gamma alumina catalyst was prepared byadding an aqueous solution of copper nitrate to calcium doped gammaalumina (Saint-Gobain Norpro, Ohio) using an incipient wetnessimpregnation technique to achieve a target copper loading of 2 wt %. Thecatalyst was dried overnight under vacuum at 110° C. and calcined at400° C. under flowing air for 6 hours.

Example 4

Copper nitrate (Acros, Geel, Belgium) was added to a silica support(Davisil, grade 635, Sigma Aldrich, St Louis, Mo.) using an incipientwetness impregnation technique to achieve a target Cu loading of 5 wt %.The catalyst was dried in an oven with an air purge at 120° C. and thencalcined in the same oven with a temperature ramp of 2° C./min to 550°C. and held for 7 hours.

Example 5

Raney copper (W. R. Grace) was directly used in the ethanoldehydrogenation testing after water washing and H₂ co-feed over thecatalyst overnight.

Example 6

Copper-zinc-aluminate (Sud-Chemie, ShiftMax 230) was sized to 18×30 meshand used directly in ethanol dehydrogenation testing.

Ethanol Dehydrogenation Example 7

The catalyst systems referenced in Examples 1-6 were investigated fordehydrogenation of ethanol. The studies were conducted in a 8.5 mminternal diameter size stainless steel tube reactor. 22 grams ofcatalyst were loaded into the reactor. In all cases, the catalyst wasreduced at 350° C. under flowing hydrogen prior to use. A feedstockconsisting of 95% ethanol in water was then passed over the catalystunder the conditions shown in Table 5.

The gas, organic (when present) and aqueous phases were collected andanalyzed to determine product yields. Table 5 shows the reactionproducts as a function of operating conditions for the catalystsdescribed in Examples 1 to 6. The overall extent of dehydrogenation canbe gauged by the hydrogen yield, ranging from 0.18 to 0.84 moles ofhydrogen produced per mole of ethanol fed.

Several reaction pathways are evident from the product profiles, due tofunctionality inherent in both the copper metal function and thesupports. These reaction products were mixtures of oxygenates suitablefor further processing into hydrocarbons. Importantly, the H:C_(eff)ratio of the oxygenate mixtures were lower than that of the feed alkanolin all cases.

TABLE 5 Ethanol Dehydrogenation over Catalysts in Examples 1-6 2% 5% Cu/1% 2% 5% 5% Cu/ Ca - 5% Shift Cu/ Cu/ Cu/ Cu/ γ- γ- Cu/ Raney MaxCatalyst mZrO2 mZrO2 mZrO2 mZrO2 Al2O3 Al2O3 SiO2 Cu 230 WHSV wt_(feed)/1.5 0.75 1.5 1.5 0.75 0.75 0.75 0.77 0.77 (wt_(catalyst) hr) DiluentmolN₂/ 0.11 0.22 0.11 0.11 0.11 0.22 0.11 0.11 0.11 Nitrogen mol_(feed)Temperature ° C. 350 350 300 350 300 350 350 325 300 Pressure Psig 100100 100 100 100 100 100 100 100 Hydrogen molH₂/ 0.18 0.52 0.60 0.78 0.580.48 0.80 0.84 0.82 yield mol_(feed) Ethanol % 71.5 94.6 77.9 97.4 87.385.7 64.3 56.9 58.1 conversion Product Yields, carbon contained withincategory as percent of feed carbon Acetaldehyde 17.5 16.2 3.0 6.0 3.322.0 20.5 14.3 9.4 Ketone 4.2 11.9 9.6 36.3 7.9 5.1 — 0.9 0.9 AceticAcid 4.0 4.3 4.5 4.8 2.5 1.2 11.1 18.6 21.9 Ethyl Acetate 18.5 16.9 45.214.5 31.1 16.2 21.7 31.1 20.1 Diethyl Ether 6.5 — 0.02 0.5 11.1 3.8 — —— Alcohol (excluding 14.5 15.9 11 11.4 24.0 19.4 1.1 0.6 0.4 ethanol)Olefin 3.0 3.8 0.1 0.6 4.5 2.4 0.1 0.1 0.1

Dehydrogenation and Condensation of Ethanol Using Copper and AcidicCatalysts

The following examples illustrate a process for dehydrogenating analkanol feed to oxygenated hydrocarbons, followed by the conversion ofthe oxygenates to hydrocarbons across a condensation catalyst.

A commercially available Al₂O₃ bound ZSM-5 support ( 1/16″ extrudates,20% Al₂O₃ Binder, ZSM-5 SAR 30, Zeolyst) was employed in theseexperiments.

Example 8

Nickel nitrate (Sigma Aldrich, St Louis, Mo.) was added to acommercially available Al₂O₃-bound ZSM-5 support ( 1/16″ extrudates, 20%Al₂O₃ Binder, ZSM-5 SAR 30, Zeolyst) using excess water and evaporatingthe water while heating at 60° C. under vacuum and rotating in a roundbottom flask until dry to achieve a target Ni loading of 1 wt %.

Example 9 Comparative Example without Dehydrogenation

An Inconel reactor with an internal diameter of 0.369 inches was loadedwith the catalyst from Example 8 to a catalyst bed depth of 18 inches.The catalyst was reduced with H₂ at atmospheric pressure flowing atapproximately 800 ml/min and the temperature was ramped from 25° C. to370° C. in 3 hours. Once at temperature, the reactor was pressurizedwith H₂ to 100 psig and then a 70% ethanol (in DI water) mixture was feddown flow into the reactor at a WHSV of 1.9 g ethanol/g catalyst/hour.Once steady state conditions were achieved, an analysis of reactionproducts was completed. The gas products were analyzed by means of a gaschromatograph equipped with a flame ionization detector, the aqueousphase products were analyzed for total carbon, and the organic phasecomponents were analyzed using a gas chromatograph equipped with bothflame ionization and mass spectrometry detectors. The results obtainedfrom this experiment are displayed in Table 6.

Example 10

An Inconel reactor with an internal diameter of 0.87 inches with anInconel thermowell with an OD of 0.1875 inches running through thecenter of the reactor was loaded as a stacked bed with catalyst fromExamples 4 (top catalyst, 4.25 inches) and 8 (bottom catalyst, 8.5inches), separated by a thin layer of quartz wool. The catalyst wasreduced with H₂ at atmospheric pressure flowing at approximately 800ml/min and the temperature was ramped from 25° C. to 350° C. in 3 hours.Once at temperature, the reactor was pressurized with H₂ to 125 psig,and then a 70% ethanol (in deionized water) mixture was fed down flowinto the reactor at a WHSV of 1.1 g ethanol/g ZSM-5 catalyst. Oncesteady state conditions were achieved, an analysis of reaction productswas completed. The gas products were analyzed by means of a gaschromatograph equipped with a flame ionization detector, the aqueousphase products were analyzed for total carbon, and the organic phasecomponents were analyzed using a gas chromatograph equipped with bothflame ionization and mass spectrometry detectors. The results obtainedfrom this experiment are displayed in Table 6.

Example 11

An Inconel reactor with an internal diameter of 0.369 inches was loadedas a stacked bed with catalyst from Examples 2 (top catalyst, 9.5inches) and 8 (bottom catalyst, 9.5 inches), separated by a thin layerof quartz wool. The catalyst was reduced with H₂ at atmospheric pressureflowing at approximately 800 ml/min and the temperature was ramped from25° C. to 370° C. in 3 hours. Once at temperature, the reactor waspressurized with H₂ to 100 psig, and then a 70% ethanol (in DI water)mixture was fed down flow into the reactor at a WHSV of 1.9 g ethanol/gZSM-5 catalyst. Once steady state conditions were achieved, an analysisof reaction products was completed. The gas products were analyzed bymeans of a gas chromatograph equipped with a flame ionization detector,the aqueous phase products were analyzed for total carbon, and theorganic phase components were analyzed using a gas chromatographequipped with both flame ionization and mass spectrometry detectors. Theresults obtained from this experiment are displayed in Table 6.

TABLE 6 Dehydrogenation and Condensation of Ethanol Using Copper andAcidic Catalysts Example Experiment Example 9 10 Example 11 Ethanol None5% Cu on 5% Cu on Dehydrogenation SiO₂ Gamma Catalyst AluminaCondensation 1% Ni on 1% Ni on Al₂O₃ Bound Catalyst Al₂O₃ Al₂O₃ ZSM-5Bound Bound ZSM-5 ZSM-5 Organic Phase % of feed 55 69 59 Yield carbonHydrogen Moles of H₂ 0.03 0.42 0.10 Production produced/mole of carbonfed Total Aromatic % of feed 41 57 50 Production carbon Total Paraffin %of feed 49 29 42 Production carbon

Control of Alkanol Dehydrogenation Extent through Bypass ofDehydrogenation Catalyst

In certain cases it may be advantageous to feed a portion of the feedalkanol directly to the condensation catalyst without passing over adehydrogenation catalyst. This allows fine control over the averageextent of dehydrogenation.

Example 12

An Inconel reactor with an internal diameter of 0.87 inches with anInconel thermowell with an OD of 0.1875 inches running through thecenter of the reactor was loaded in a stacked bed configuration withcatalyst from Examples 4 and 8. A thermowell with an OD of 0.1875 incheswas placed on the centerline of the bottom bed of catalyst from Example4. Said catalyst was loaded to a length of 8.5 inches. The top catalyst,from Example 8, was loaded to a length of 8.5 inches. The two beds ofcatalyst were separated by a thin layer of quartz wool and approximately2 inches of inert packing material. Two feed lines and two HPLC pumpswere installed to supply feed to both beds of catalyst. One feed lineentered through the head of the reactor and the second line extendedthrough the top bed of catalyst to bypass feed to the conversioncatalyst. The entire catalyst bed was reduced at atmospheric pressureflowing at approximately 800 ml/min of H₂ and temperatures were rampedfrom 25° C. to 370° C. in 3 hours. Once at temperature, the reactor waspressurized with H₂ to 100 psig and then a 70% ethanol (in deionizedwater) mixture was fed down flow into the reactor at a WHSV of 1 gethanol/g ZSM-5 catalyst/hour. Once steady state conditions wereachieved, an analysis of reaction products was completed. The ethanolfeed was split between the top and bottom in ratios of 1:1, 2:1, and 1:2and an oxidative regeneration was performed between weight checks ateach feed split ratio. The gas products were analyzed by means of a gaschromatograph equipped with a flame ionization detector, the aqueousphase products were analyzed for total carbon, and the organic phasecomponents were analyzed using a gas chromatograph equipped with bothflame ionization and mass spectroscopy detectors. The results obtainedfrom this experiment are displayed in Table 7.

Example 13

Example 12 was repeated at 300 psig. All other details specific to theexperimental set-up and operation remained the same. The resultsobtained from this experiment are displayed in Table 7.

TABLE 7 Dehydrogenation and Condensation of Ethanol Using Copper andAcidic Catalysts Experiment Example 9 Example 12 Example 13 Ethanol None5% Cu on SiO₂ 5% Cu on SiO₂ Dehydrogenation Catalyst Condensation 1% Nion 1% Ni on Al₂O₃ 1% Ni on Al₂O₃ Catalyst Al₂O₃ Bound ZSM-5 Bound ZSM-5Bound ZSM-5 Pressure Psig 100 100 300 Feed Split RatioDehydrogenation:Condenstation 0:1 2:1 1:1 1:2 2:1 1:1 1:2 Organic Phase% of feed carbon 55 60 56 57 62 53 58 Yield Hydrogen Moles of H₂ 0.030.19 0.13 0.08 0.11 0.09 0.06 Production produced/mole of carbon fedTotal Aromatic % of feed carbon 41 57 52 49 51 45 43 Production TotalParaffin % of feed carbon 49 39 39 42 38 48 46 Production

The invention claimed is:
 1. A method of converting alkanols to aromatichydrocarbons, the method comprising: partially dehydrogenating a C₁-C₆alkanol feedstock in the presence of a dehydrogenation catalyst at aneffective dehydrogenation temperature and an effective dehydrogenationpressure to produce a mixture of oxygenate components comprising (a) anunreacted C₁-C₆ alkanol and (b) a carboxylic acid, an aldehyde, anester, or any combination thereof, wherein at least a portion of theoxygenate components in the mixture have a hydrogen to carbon effectiveratio of less than 1.6, and wherein the feedstock is dehydrogenated toan extent sufficient to result in the mixture of oxygenate componentshaving a total hydrogen to carbon effective ratio of between 1.2 and1.6; and exposing the mixture of oxygenate components to an oxygenateconversion catalyst at an oxygenate conversion temperature and anoxygenate conversion pressure to produce aromatic hydrocarbons.
 2. Themethod of claim 1, wherein the mixture of oxygenate components comprisesthe carboxylic acid and wherein the carboxylic acid has a hydrogen tocarbon effective ratio of less than 1.6.
 3. The method of claim 2,wherein the carboxylic acid is acetic acid.
 4. The method of claim 1,wherein the mixture of oxygenate components comprises the ester andwherein the ester has a hydrogen to carbon effective ratio of less than1.6.
 5. The method of claim 4, wherein ester is ethyl acetate.
 6. Themethod of claim 1, wherein the mixture of oxygenate components comprisesthe aldehyde and wherein the aldehyde has a hydrogen to carbon effectiveratio of less than 1.6.
 7. The method of claim 6, wherein the aldehydeis acetaladehyde.
 8. The method of claim 1, wherein the C₁-C₆ alkanolfeedstock comprises two or more C₁-C₆ alkanols.
 9. The method of claim1, wherein the C₁-C₆ alkanol feedstock comprises methanol, ethanol,propanol, butanol, or combinations thereof.
 10. The method of claim 1,wherein the C₁-C₆ alkanol feedstock comprises ethanol.
 11. The method ofclaim 1, wherein the total hydrogen to carbon effective ratio is lessthan 1.5.
 12. The method of claim 11, wherein the dehydrogenationcatalyst comprises: (i) a metal selected from the group consisting ofCu, Ru, Ag, CuCr, CuZn, Co, Raney copper, copper-zinc-aluminate, alloysthereof, and combinations thereof; and/or (ii) a support selected fromthe group consisting of alumina, silica, silica-alumina, titania,carbon, zirconia, zinc aluminate, and mixtures thereof.
 13. The methodof claim 1, wherein: (i) the dehydrogenation temperature is betweenabout 80° C. and 500° C.; and/or (ii) the dehydrogenation pressureranges from below atmospheric pressure to about 1000 psig.
 14. Themethod of claim 1, wherein the oxygenate conversion catalyst comprises azeolite.
 15. The method of claim 14, wherein the oxygenate conversioncatalyst: (i) is ZSM-5; (ii) is modified by a material selected from thegroup consisting of phosphorous, gallium, zinc, nickel, tungsten, andmixtures thereof; and/or (iii) contains a binder selected from the groupconsisting of alumina, silica, silica-alumina, titania, zirconia,aluminum phosphate, and mixtures thereof.
 16. The method of claim 1,wherein: (i) the oxygenate conversion temperature is between about 250°C. and 550° C.; and/or (ii) the oxygenate conversion pressure rangesfrom less than atmospheric pressure to about 1000 psig.
 17. A method ofconverting alkanols to aromatic hydrocarbons, the method comprising:partially dehydrogenating a C₁-C₆ alkanol feedstock in the presence of adehydrogenation catalyst at an effective dehydrogenation temperature andan effective dehydrogenation pressure to produce a mixture of oxygenatecomponents comprising a C₁-C₆ alkanol, a carboxylic acid, an aldehyde,and an ester, wherein the carboxylic acid, the aldehyde, and the esterhas a hydrogen to carbon effective ratio of less than 1.6, and whereinthe feedstock is dehydrogenated to an extent sufficient to result in themixture of oxygenate components having a total hydrogen to carboneffective ratio of between 1.2 and 1.6; and exposing the mixture ofoxygenate components to an oxygenate conversion catalyst at an oxygenateconversion temperature and an oxygenate conversion pressure to producearomatic hydrocarbons.
 18. The method of claim 17, wherein the C₁-C₆alkanol feedstock comprises ethanol, the carboxylic acid comprisesacetic acid, the aldehyde comprises acetaladehyde, and the estercomprises ethyl acetate.
 19. The method of claim 17, wherein the mixtureof oxygenates further comprises a ketone, an ether, or both a ketone andan ether.
 20. The method of claim 17, wherein the mixture of oxygenatesconsists essentially of the C₁-C₆ alkanol, the carboxylic acid, thealdehyde, and the ester.
 21. The method of claim 17, wherein the mixtureof oxygenates consists essentially of (i) the C₁-C₆ alkanol, thecarboxylic acid, the aldehyde, the ester, and (ii) a ketone, an ether,or both a ketone and an ether.
 22. The method of claim 17, wherein thetotal hydrogen to carbon effective ratio is less than 1.5.